The Free Press, Mankato, MN

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January 17, 2010

Fine for now, winterkill could hit area lakes

By John Cross Free Press Staff Writer

WATERVILLE — The heavy blanket of snow that has hampered ice anglers’ efforts to get around also may threaten the fish populations of some area lakes in coming weeks.

Hugh Valiant, manager of the Minnesota Department of Natural Resources Waterville Fish Hatchery, said that some of the shallower lakes in southern Minnesota may suffer winterkill — a phenomenon that causes fish to suffocate as the heavy snow cover shuts down the oxygen-infusing photosynthetic process in aquatic plants.

Fisheries crews began sampling oxygen levels in area lakes and while deeper lakes and most shallow lakes equipped with aeration systems seem to be holding up, oxygen levels in some shallow lakes have dropped to critical levels, Valiant said.

Typically, lakes are in danger of suffering a winterkill event when dissolved oxygen levels fall to about 1 part per million or less, he said.

Among the area lakes in imminent danger are Cody-Phelps and Pepin Lakes in Rice County, Lake Ida in Blue Earth County, and Dora Lake in Le Sueur County.

Valiant said that many shallow lakes in the area equipped with aeration systems are holding up well and even some winterkill-prone lakes equipped without such systems seem to be doing fine.

Among them, Lake Henry in Le Sueur County, a shallow lake the DNR uses for a walleye rearing pond, had oxygen levels in the 7 ppm range.

Indeed, several dozen fish houses are spread across the lake, presumably targeting walleyes that were missed by DNR seining crews, Valiant said.

One notable exception is Loon Lake in Waseca County were oxygen levels have dropped precipitously in spite of an operating aeration system.

There are indications fish are being stressed.

Lakes in imminent danger of winterkill typically are open to liberalized fishing regulations that permit anglers to harvest fish without regard to limit using a variety of means.

However, as of Saturday, no area lakes had been listed on the DNR Web site as open to liberalized fishing regulations.

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